Active optical pre-compensation in short range frequency transfer in optical single-mode fiber

Short distance fiber based optic distribution of time and frequency is often considered sufficiently stable and therefore, uncompensated one way transfer is used. However, when fiber distances increase to a few km, and a substantial amount of the fiber is installed outdoors or in aisles and attics without temperature control, the delay through the fiber may vary substantially. Since the variations are slow, a microwave frequency modulated on an optical carrier may be assumed to remain sufficiently stable. The time delay through the fiber will nevertheless depend on the extremes of the temperature variation which must be taken into account or compensated for. This study presents the design issues of a real time compensation and some results of an optical compensation technique.